Treatment of vegetable tissue



Patented June 28, 1949 Clarence Birdseye, Gloucester, Mass., assignor to Dehydration, Inc., Gloucester, Mass, a corporation of Massachusetts No Drawing. Original application June 21, 1944, Serial No. 541,459. Divided and this application March 21, 1945, Serial No. 584,033

4 Claims. (Cl. 99-'-221) This invention has for its primary objective the production of blanched quick-frozen or dehydrated vegetable matter retaining its original nutrient and flavoring elements more fully than is possible when such vegetable matter is blanched in either water or steam in accordance with current commercial practices. More specific objects of the invention are to permit the blanching of fruits without causing them to take on a cooked appearance and flavor; to blanch vegetables with substantially no loss of any of their water-soluble elements; to facilitate penetration into vegetable units of edible materials which have been applied to the exterior thereof before blanching; to regulate and control loss of weight during blanching; to provide facilities for both blanching and dehydrating continuously in the same apparatus; and in general to produce frozen and dehydrated vegetables and fruits of high quality in an efiicient a 2 to be frozen or dehydrated are first given a treatment with hot water or steam to inactivate their enzyme (particularly catalase and perioxidase) content. known as blanching and usually consists in raising the temperature of all parts of the material to at least 185 F. and maintaining that temperature in the product for at least five seconds. Many types of commercial blanching apparatus are available, and all of them use either water at or near the boiling point or steam at atmospheric or greater pressures. Blanching is so well understood and so universally applied in the processing of vegetables for freezing and dehydrating that details of the procedure need notbe described herein. However, there is given below a table of standard blanching times with both hot waterand steam as a blanching medium for a number of common vegetables, as recommended on pages 13 and 14 of the 1940 issue of the Refrigerating Data Book:

This treatment has for many years been Vegetable Varieties Best Suited fi ggigg g'gg gffig f 60. Beans, green shell French horticultural St 105. I Beets- Crosb 1% in. diam. 150' Over y 2 in. diam. cooked. Beet greens do 2. Carrots, sliced (56 in.) Nantes 30. Curly mustard Giant Southern Curled Mustard. Kale Tall Curled Scotch Kale Kohlrabi, diced Early White Vienna st am New Zealand spinach {2 Swiss chard Tmmfllnq 120. Turnips, diced Purple Top White Globe {gg water g8: Aspmagusn nn nu Washington Steam 3 ,1 3 33%;; l v Small beans, 1. Beans, lime Henderson Boiling water Medium beans, 1%.

. 7 Large beans, 2.

Kentucky Wonden. Beans, snap Blue Lake ....do 2.

Wisconsin Refugee Small pieces, 3. Broccoli Italian Green Sprouting ..d0 Medium pieces, 4%. Large p eces, 5. Cauliflower Snowball d0 gfii g g zag 4 Small new, V. Peas {Large peas, 1

Spinach l. 2%.

Small cars 6. 8-row Golden Bantam. S Sweet com {Golden llantam... team {figgi g g ia 14'row 0 en antam t Golden Bantam.--

blanching is that if the product units are to be 7 evenly blanched, they must be either spread in a very thin, uniform layer or must be thoroughly stirred throughout the blanching process. Stirring during blanching is sometimes highly undesirable; for it inevitably abrades, or even breaks, the units of such delicate vegetables as white and sweet potatoes.

Another" objectionable feature of present methods is thatfacilities for such blanching cannot readily be incorporated as an integral part of a dehydrating apparatus. Still another 'undesirable characteristic of present blanching practice is that when vegetables and fruits are blanched in hot water or steam, it is necessary to overheat the surface areas of the product units condensed onto the product from that atmoslphere.

By the process of my co-pending application Serial No. 536,422, vegetables intended for dehydration are first drenched with very hot water, next treated with a cooler solution containing edible materials to be added to the vegetables, and then blanched. The edible material penetrates into the vegetable units as their tissues are killed by the heat of blanching. If, however,

a steam blanch is used, water condensed from the steam upon the vegetables dilutes and partly washes away the film of edible solution previ-'- ously applied. This necessarily results inimperfect penetration into the product by the edible materials contained in the solution. My present method of blanching by high-frequency heat .generated in the product itself completely eliminates the foregoingdifliculties.

Certain fruits (e. g. strawberries) are seriously damaged by excessive heat and can be safely blanched only by prolonged-heating at 7 low temperatures; e. g. two to four minutes at (or of the mass of units, if blanching is done by heating an aggregation of units) in order to heat Cubed white potatoes the interior of. the'units to the temperature re- 'quired for enzyme inactivation. For example,

handled gently during subsequent processing.

Sliced ripe fruits, for either freezing or dehydrating, become mushy on the surfaceif blanched in either hot water or steam.

I have discovered that all of the shortcomings 175 F. I prefer to subject suchfruits intermittently to the action of high-frequency fields. By this means the entire unit of product can, without danger of overheating, be alternately brought to any desired temperature, allowed to cool slightly, and then again heated to the maximum temperature desired. Moreover, by my method of alternately heating and cooling as described above, even heat-sensitive'products may be safely not only blanched, but actually pre-cooked to any desired degree.

Many fruits, for example berries and sliced peaches, are improved in color, flavor, consistency, and aroma if they are blanched while coated with edible material, such as sugar; a neutral sugai salt film, an acid protecting film or glycerine and acetic acid, or some other edible substance which protects the surface of o the fruit from oxidation both during and after of present blanching methods can be overcome by the use of heat generated directly within the vegetable units by high-frequency electric fields. In such fields the temperature of the product is rapidly raised to the desired point throughout itsmass. Heat generated in the product in this manner permits effective, uniform and accurate blanching without bringing any extraneous water into contact with the surfaces of the product units, and thus avoids completely the leaching action of hot water and steam. Moreover, no stirring of the product during blanching is required; for heating is uniform throughout the mass regardless of the thickness of the mass.

Another advantage of my present invention is that moisture loss from the product during blanching can be accurately controlled merely by regulating the'humidity of the gas surrounding the product-during the blanching process. For if the product layer is relatively thin and if the surrounding atmosphere is arid, considerable moisture will be evaporated from the product during the blanchingprocess. If, on the contrary, the product layer is quite (several inches) thick and if the atmosphere surrounding the product has a relative humidity of approximately 100. per cent, no moisture can be lost during blanching. Moreover, since the product will at all times during blanching be hotter than the surrounding atmosphere, no moisture can be present invention, however, the fruit and the blanching and also penetrates into the fruit by osmosis to firm the fruit tissue. Neither steam nor hot water can be used satisfactorily for blanching such coated fruits, for the water removes or dilutes much of the coating. But

blanching in a high-frequency electric. field, in-

accordance with my present'invention, does not bring extraneous water into contact with the coating on the fruit and does facilitate penetration of the coating into the product.

v In certain instancese. g. ripe plumsit is desirable to blanch the product while submerged in a protective solution, such as sugar syrup,

the product being blanched by heat transferred to it from the hotsyrup. This type of blanching has been tried experimentally but has not come into commercial use, because the fruit is overheated at its surface before it is sufiiciently heated at its center. By the method of my protective substance in which it'is submerged are simultaneously heated throughout by the action of the high-frequency electric field in which they are placed. Thus my invention for the first time makes blanching in a' sugar syrup or other liquid commercially practicable.

As pointed out in my co-pending application Serial No. 536,422, it is often desirable to add an alkaline substance-e. g. sodium bicarbonate-- v to vegetable tissue for the purpose of tenderizing it. Anobjection to this methodmf rendering dehydrated vegetable tissue tender is that only very limited amounts of the alkaline substance their natural enzyme content, and then-either V before, during or after dehydration-treated with and caused to absorb a proteolytic enzyme, such as pepsin or papain, or another suitable active enzyme. I prefer to accomplish this by blanching the vegetable tissue in a highfrequency electric field to inactivate enzymes found in the living tissue, removing approximately 60 percent of the moisture from the blanched tissue, causing the partially dehydrated tissue to absorb an aqueous solution of the proteolytic enzyme, and then further dehydrating the vegetable.

The process of my'present invention can be applied as a preliminary treatment for vegetable tissue which is to be either frozen or dehydrated. When the product is to be dehydrated, I prefer to use an apparatus of the type disclosed in my co-pending application Serial No. 456,903, filed Sept. '1, 1942, now Letters Patent No. 2,419,876, dated April 29, 1947. In that case I use dielectric material for the top belt of the apparatus and preferably pass the product on that ,belt repeatedly through high-frequency fields before it is subjected to the hot gas, radiant energy, and conducted heat which characterize the said apparatus. Depending upon the type of installation desired, the blanching may take place on the top belt either before or immediately after the product enters the uppermost tunnel in the apparatus. In certain instances where the product pieces are relatively resistant to breakage or abrasion even after being blanched (e. g. carrots), I may positively stir the product mass while it is passing from one high-frequency field to the next thus accelerating the evaporation of moisture from the product and the consequent cooling ofthe product units. When vegetable tissue is to be frozen, I have found that it is sometimes advantageous to place the tissue in a consumer package and then blanch the tissue in the package by heating both tissue and package in a high-frequency electric field.

EXAMPLES OF PROCESS Sliced apples Pare and core sound, ripe apples ofany variety, cut into eighths, dip in a light sugar syrup by weight), place in a three-inch layer on a belt ing is required, repeat the alternate heating and cooling until the desired degree of pre-cooking has been attained. After the foregoing treatment has been completed, the product pieces may be either frozen before or after packaging, or dehydrated in an apparatus according to the disclosure of my prior Patent No. 2,419,876.

Dehydrated cabbage Core and shred cabbage in the usual manner. Place the shredded product in a 3-inch layer on an endless woven-wire, stainless-steel belt,

shower with boiling water for approximately three seconds, drain for ten seconds, shower with a F. aqueous solution containing of 1 per cent each of sodium bicarbonate and sodium sulphite and 25 per cent glycerine by weight, drain for twenty seconds, transfer to a layer three inches thick on an endless belt of woven asbestos fibers impregnated with a synthetic resin, and pass through a high-frequency field of approximately 15 to 25 megacycles per second until the temperature of the product mass has been raised substantially uniformly'to approximately 200F. Then, without allowing the blanched product to cool substantially, run it onto the uppermost belt of a dehydrating apparatus sim- 'ilar to that disclosed in my prior patent above identified. In the dehydrating apparatus, dry the cabbage to a residual moisture content of approximately 4 per cent. Then remove the dried cabbage from the dehydrator and package in moisture-vapor-proof cellophane or other material equally impervious to the passage of moisture vapor at room temperature.

In dehydrating cabbage and other leafy vegetables, it is desirable to 'compact the product before blanching it in order to reduce the volume of the product and the thickness of the layer which must be passed between the electrodes creating the high-frequency. field. This is important because power cost runs up as the distance between the electrodes increases. Accordingly, in carrying out my process I may proceed by advancing the leafy vegetable in a loose layer upon a conveyor belt and then compact this layer by passing it between rollers on its way to the high-frequency blanching field.

In blanching fruit or other products in a liquid syrup, I have found it advisable to provide for actual electrical contact between the electrodes and the liquid in which the fruit is immersed since by so doing I am able to achieve a faster and more economical blanching operation. This constitutes a further novel step of my process and may be effected by providing the uppermost electrode with drag wires or strips which will enter the liquid solution as the product being treated is passed between the electrodes.

I have referred'hereinabove to the treatment of various vegetable units by immersing or spraying them with a solution containing various agents for protectingor improving the product. I contemplate, however, treating fruit or vegetable units by a dry process of dusting with powder; for example, I may mix powdered sugar, sodium sulphite, and sodium bicarbonate in the proper proportions and dust the cut vegetable units with this powdered mixture before subjecting them to the action of a high-frequency electric field. In this way I cause the powdered agents to penetrate into the vegetable tissue after it has been killed. in the blanching step, and all this is effected without any leaching or diluting tendency, and, if desired, simultaneously with an initial stage of dehydration.

The present application is a division of my copending application Serial No. 541,459, filed June 21, 1944.

Having thus disclosed my invention and described in detail several examples of its practice in the treatment of illustrative products, I claim as new and desire to secure by Letters Patent:

1. In the preparation of vegetable tissue for further processing, the steps of heating the tissue in a high frequency electricfield thereby blanching the tissue and inactivating its natural enzyme v 4' I content without leaching action, simultaneously removing moisture from the blanched tissue by surrounding it with an arid atmosphere, coating the tissue with a solution containing a proteolytic enzyme and thereby causing the tissue to absorb the enzyme solution thus added, and then dehydrating the tissue.

-2. In the preparation of vegetable tissue for further processing, the steps of heating the tissue in a high frequency electric field and in an atmosphere of predetermined humidity thereby blanching it without leaching action and controlling the moisture loss from the tissue during the blanching operation and then coating the blanched tissue with an aqueous solution oi. an active protcolytic enzyme thereby causing the tissue to be penetrated by an additional and diflerent enzyme from that originally contained.

3. In the preparation of vegetable tissue for further processing, the steps of first coating the tissue with a sugar-containing film, and then blanching the tissue by heating the tissue in a high frequency electric field thereby blanching it without leaching action and without dilution of its said coating, and adding a proteolytic enzyme to the blanched tissue.

4. A process of improving and preserving vegetable tissue which includes the steps of first coating the tissue with sodium bicarbonate. then heating the tissue in a high frequency electric field and in an arid atmosphere thereby blanching the tissue without leaching action and at the same time removing approximately 60% of the initial moisture content of the tissue, then causing the partially dehydrated tissue to absorb an The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,214,598 Shaflner Feb. 6, 191'! 2,072,955 Lunt Mar. 9, 1937 2,340,170 Baer Jan. 25, 1944 OTHER REFERENCES Thermex High Frequency Heating," pub. by the Girdler Corp., Louisville, Ky., 1942, page 9.

Modern Packaging," Feb. 1944, by v. w. Sherman. 

